Efficient way to check if std::string has only spaces

Question

I was just talking with a friend about what would be the most efficient way to check if a std::string has only spaces. He needs to do this on an embedded project he is worki

Answer 1

I do not approve of you const_casting above and using strtok.

A std::string can contain embedded nulls but let's assume it will be all ASCII 32 characters before you hit the NULL terminator.

One way you can approach this is with a simple loop, and I will assume const char *.

bool all_spaces( const char * v )
{
   for ( ; *v; ++v )
   {
      if( *v != ' ' )
          return false;
   }
   return true;
}

For larger strings, you can check word-at-a-time until you reach the last word, and then assume the 32-bit word (say) will be 0x20202020 which may be faster.